feat(apple): local notifications for transfer lifecycle events

Adds background notifications for the "the thing you were waiting for is
done" moments, alongside the existing incoming-approval-request one:

  - a receive finished downloading            (receive -> done)
  - a receive failed / was interrupted         (receive -> failed)
  - a share you own failed                      (send -> failed)
  - a receiver finished downloading your share  (receiver status completed)

A new TransferNotificationCoordinator observes core state + signals and
publishes these; the decision of which moments notify is a pure function
(plannedTransferNotifications / plannedReceiverNotifications), unit-tested
independently. The first state snapshot only primes existing history as seen
so launch doesn't spam.

Notification permission is now the single source of truth. The in-app
notifications toggle and its decoupled UserDefaults preference are gone;
the Settings section shows an "Allow notifications" button that requests the
OS permission (or deep-links to Settings once decided), and notifications
gate purely on `permission == .granted`.

macOS delivery fixes:
  - add a UNUserNotificationCenterDelegate so banners present even while the
    app is active (the app window is usually open on macOS)
  - present-when-active on macOS, suppress-when-foregrounded on iOS
  - reserve the notification id before awaiting publish: the CombineLatest
    fired several times and re-added the same identifier, which macOS
    coalesces into a silent update with no banner
  - LocalNotificationService seeds its permission at init so gating can't
    race a not-yet-refreshed .notDetermined

Eight localized title/body strings added (apple-only); the shared
notifications_description copy is generalized from "receive requests" to
"transfer activity".

apple/Tests/AppPreferencesRepositoryTests.swift

@@ -19,7 +19,6 @@ final class AppPreferencesRepositoryTests: XCTestCase {
 		let repo = AppPreferencesRepository(defaults: defaults(), fallback: fallback())
 		XCTAssertEqual(repo.preferences.username, "Default")
 		XCTAssertEqual(repo.preferences.themeMode, .system)
-		XCTAssertFalse(repo.preferences.notificationsEnabled)
 	}
 
 	func testValuesPersistAndReload() {
@@ -28,14 +27,12 @@ final class AppPreferencesRepositoryTests: XCTestCase {
 		let repo = AppPreferencesRepository(defaults: store, fallback: fb)
 		repo.setUsername("Bob")
 		repo.setThemeMode(.dark)
-		repo.setNotificationsEnabled(true)
 		repo.setReceiveFolder(ReceiveFolder(kind: .iosSecurityScopedUrl, value: "file:///x", displayName: "Custom"))
 
 		// A fresh repository over the same store reflects the persisted values.
 		let reloaded = AppPreferencesRepository(defaults: store, fallback: fb)
 		XCTAssertEqual(reloaded.preferences.username, "Bob")
 		XCTAssertEqual(reloaded.preferences.themeMode, .dark)
-		XCTAssertTrue(reloaded.preferences.notificationsEnabled)
 		XCTAssertEqual(reloaded.preferences.receiveFolder.displayName, "Custom")
 		XCTAssertEqual(reloaded.preferences.receiveFolder.kind, .iosSecurityScopedUrl)
 	}

apple/Tests/ApprovalCoordinatorTests.swift

@@ -11,7 +11,6 @@ final class ApprovalCoordinatorTests: XCTestCase {
 	private func makeCoordinator(_ core: FakeCoreGateway) -> ApprovalCoordinator {
 		ApprovalCoordinator(
 			repository: core,
-			preferences: Fixtures.preferences(),
 			notifications: LocalNotificationService(),
 			visibility: AppVisibility(),
 			messages: UiMessageController()

apple/Tests/TransferNotificationTests.swift

@@ -0,0 +1,44 @@
+import XCTest
+@testable import VniDrop
+
+@MainActor
+final class TransferNotificationTests: XCTestCase {
+
+	func testTransferNotificationsFireForTerminalStatesOnly() {
+		let transfers = [
+			Fixtures.transfer(id: 1, direction: .send, status: .failed),
+			Fixtures.transfer(id: 2, direction: .receive, status: .done),
+			Fixtures.transfer(id: 3, direction: .receive, status: .failed),
+			Fixtures.transfer(id: 4, direction: .receive, status: .receiving),  // in-flight, ignored
+			Fixtures.transfer(id: 5, direction: .send, status: .sharing),       // active share, ignored
+			Fixtures.transfer(id: 6, direction: .send, status: .done),          // send-done isn't notified
+		]
+		let planned = plannedTransferNotifications(transfers, published: [])
+		XCTAssertEqual(planned.map(\.kind), [.sendFailed, .receiveCompleted, .receiveFailed])
+		XCTAssertEqual(planned.map(\.id), ["send-failed-1", "receive-completed-2", "receive-failed-3"])
+		XCTAssertEqual(planned.first?.transferName, "Photos")
+	}
+
+	func testTransferNotificationsSkipAlreadyPublished() {
+		let transfers = [Fixtures.transfer(id: 2, direction: .receive, status: .done)]
+		XCTAssertTrue(plannedTransferNotifications(transfers, published: ["receive-completed-2"]).isEmpty)
+	}
+
+	func testReceiverNotificationsFireOnlyForCompletedReceivers() {
+		let requests = [
+			Fixtures.request(id: "a", requestedAt: 1, status: .completed),
+			Fixtures.request(id: "b", requestedAt: 2, status: .accepted),
+			Fixtures.request(id: "c", requestedAt: 3, status: .requested),
+		]
+		let planned = plannedReceiverNotifications(requests, published: [])
+		XCTAssertEqual(planned.map(\.id), ["receiver-completed-a"])
+		XCTAssertEqual(planned.first?.kind, .receiverCompleted)
+		XCTAssertEqual(planned.first?.receiver, "Peer")
+		XCTAssertEqual(planned.first?.transferName, "Photos")
+	}
+
+	func testReceiverNotificationsSkipAlreadyPublished() {
+		let requests = [Fixtures.request(id: "a", requestedAt: 1, status: .completed)]
+		XCTAssertTrue(plannedReceiverNotifications(requests, published: ["receiver-completed-a"]).isEmpty)
+	}
+}